I am not really a GBB guy, so I am biased.
I personally think the SR10 gives you eternally more options for upgrading internals.
Access to the Hop-up unit and better bucking options will be better with the SR10.
Mag compatibility as well as Mag price point will be better with an AEG as well.
So, SR10 is the way to go, IMO.

The good AEG guys can get come excellent performance out of their guns. I've no intention of opening my gearbox either and just getting to it seems a bit daunting.

Not sure where your LiPO "flames" comment comes from. I've not seen an incident posted here. Maybe we're all using good batteries and chargers?

The GBB rifles seem much easier to "gunsmith" to me, perhaps because the LM4 disassembles very much like the M4. Tweaking the valve in the bolt appears to be the general way to increase muzzle velocity -- several threads on this. A tighter barrel is a lot more work (to get the old one out) but beyond that is pretty simple as are bucking/hopup tweaks.

My LM4 shoots 390fps with 0.32g BBs with the high power bolt group. Not sure what's different about the bolt's internals. Not chronographed with 0.25g but they'll be faster. Heaver BBs have longer, more stable ranges. Conversion was removing one bolt group and sliding in the other. This bolt is marked "For Training Use Only" as the energy level out of an otherwise unmodified LM4 is 2.3 joules. 1.0 joule is universally considered a "safe" energy level for game play -- 100 meters/second with 0.20g BB. 350fps at the muzzle is just slightly more than 1.0j and the energy drops below 1.0j in just a couple of feet due to air resistance.

The GBB rifles seem much easier to "gunsmith" to me, perhaps because the LM4 disassembles very much like the M4. Tweaking the valve in the bolt appears to be the general way to increase muzzle velocity -- several threads on this. A tighter barrel is a lot more work (to get the old one out) but beyond that is pretty simple as are bucking/hopup.

Call me lazy but do you have the links to these threads? I especially need the one that increases muzzle velocity. Where can I get a high power bolt?